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3D printing: How does it work?

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3D printing is not a technology that works in one and the same way. There are indeed a multitude of processes for printing an object in 3D. If the printing techniques are different on the form, the principle always remains the same. It consists in superimposing layers of materials with a 3D printer according to the coordinates transmitted by a 3D file.

The following guide reveals the step-by-step operation of this machine, as well as the software and materials it uses according to the process used.

Operation of 3D printer

3D printing therefore works in several ways, which differ depending on the type of 3D printer used. These processes can be classified into three main groups:

● The deposit of material

● Solidification by light

● Agglomeration by gluing

These three processes operate according to the same basic principle, i. e. superimpose layers of materials according to the coordinates of a 3D file. The difference lies in the way its layers are deposited and treated, as well as the type of material used.

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For most of the processes used, the user needs:

● a 3D printer

● consumables (filament, powder…)

● a 3D file (in STL or OBJ format)

● slicing software to cut the file and send the instructions to the printer

● of a computer

The way to export files to the printer differs depending on the make and model: USB cable, Wi-Fi or SD card.

FDM or FFF

Most personal 3D printers work according to this principle. FDM is the acronym for Fused Deposition Modeling, which means “modeling by molten filament deposition”. This process, which was invented in 1988 by Stratasys, is a registered trademark. We also talk about FFF (Fused Filament Fabrication) or even MPD (Molten Polymer Deposition) which are royalty-free terms.

This technique consists in depositing layer by layer a filament of thermoplastic material melted at 200°C (on average) which, when superposed, gives shape to the object. The print head moves according to the X, Y and Z coordinates (length, width and height) transmitted by a 3D file corresponding to the 3D model of the object to be printed. For a long time limited to plastic materials such as classic PLA and ABS, 3D printing saw the arrival of new composite filaments based on metal (copper, bronze, etc.), carbon fibres and even wood.

More rarely, some machines use waxes or polycarbonates. Today, the food industry and medicine are gradually taking advantage of this technique to print food and cells by adapting the extrusion head.

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Stereolithography or SLA

Stereolitography is the first 3D printing technique to have been highlighted. If the authorship of this process is often attributed to the American Charles Hull, founder of 3D Systems, we owe this invention to three Frenchmen (Alain le Méhauté, Olivier de Witte and Jean Claude André) whose patents, although filed 3 weeks earlier (July 16, 1984), were unfortunately not renewed.

Also called SLA (Stereolithography Apparatus) this technique consists in solidifying a photosensitive liquid by means of an ultraviolet laser beam. SLA printers have four main parts: a tank that can be filled with a photopolymer liquid, a perforated platform that is lowered into the tank, ultraviolet (UV) radiation and a computer controlling the platform and the laser.

Just like the FDM, the printer first analyzes the CAD file, then, depending on the shape of the object, adds temporary fasteners to it to hold certain parts that could collapse. Then the laser will start by touching and instantly hardening the first layer of the object to be printed. Once the initial layer of the object has hardened, the platform is lowered, then a new surface layer of liquid polymer is exposed. The laser again traces a cross section of the object that instantly sticks to the hardened part below.

This process is repeated over and over again until the entire object is formed and completely immersed in the tank. The platform will then rise to reveal the finished object in three dimensions. After it has been rinsed with a liquid solvent to remove excess resin, the object is baked in an ultraviolet oven to harden the additional plastic material.

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Objects manufactured according to stereolithography generally have a good quality of finish and detail (0.0005 mm), resulting in smooth and even surfaces. Qualitatively it is one of the best 3D printing techniques currently available. The time required to create an object with this technique also depends on the size of the machine used. SLA also has the advantage of being able to produce large parts (several metres long). For these objects it will take several days, a few hours for the smallest ones.

Among these disadvantages, a higher cost than FDM and a more limited range of materials and colours due to the polymers used as raw material. Solvents and polymer liquids also emit toxic vapours during printing, so your room should be equipped with an exhaust hood for ventilation.

The polyjet process

This technology, patented by the Israeli-American company Objet Geometries Ltd (acquired in 2012 by the American Stratasys), also works on the principle of photopolymerization. In the same way, the object will be modeled in 3D with a specialized software (AutoCAD for example) then its file sent to the 3D printer.

The print heads will then drop by drop photosensitive material on a gel support, according to the coordinates transmitted by the file. Once the material is deposited, it will be exposed to an ultraviolet ray which will then harden it instantly. The operation will be repeated until the final object is obtained, then all that remains is to clean it. With an accuracy of around 0.005mm it is possible to produce objects with a high level of detail and interlocking assembly parts such as gears.

Object Geometries subsequently refined this technique by developing Polyjet Matrix. With 96 tips for each of its print heads, it is possible for the user to combine several different materials, flexible or more rigid. By allowing you to create your own composite, this process offers the possibility of printing more varied and complex objects.

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Laser sintering

This technique, created by an American student at a Texas university in 1980, was later developed (2003) by the German company EOS. Also called SLS (Selective Laser Sintering), it is also a laser printing process. This time a very powerful laser beam will merge a powder at very precise points defined by a STL file that your computer communicates to your 3D printer.

The powder particles under the effect of heat will then melt and eventually fuse together. A new layer of fine powder is then spread out and hardened again by the laser and connected to the first one. This operation is repeated several times until your part is finished. Then, your part is lifted from the loose powder and the object is brushed and then sanded or sanded by hand for finishing.

The powder most often used for this type of printing is polyamide. White in colour, this material is actually nylon. It will give your object a porous surface that can be repainted if you want to give it color. Other components such as glass powder or ceramic can also be used. Often manufacturers use a mixture of two kinds of powders to obtain more sophisticated objects.

LA 3DP

Originally developed in 1993 in Massachusetts at the Institute of Technology (MIT) in 1993, 3DP (Three-Dimensional Printing) forms the basis of Z Corporation’s 3D printing process. The process consists of spreading a thin layer of composite powder on a platform.

The print head will then deposit on it fine drops of colored glue which combined with each other allow to obtain a wide range of color. The platform lowers as the powder layers are glued together until the final object is obtained. For the finishing, it is necessary to vacuum the excess powder, brush and/or sand the part, then heat it to finalize the solidification.

The 3DP has the advantage of being fast and offering a wide range of colours. Up to 6 times cheaper than a 3D SLA printer, its price is more attractive despite its precision and sometimes inferior printing quality. Among the disadvantages, without post-printing treatment the parts are more fragile and their surface is rougher.

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